Integrated circuits are used in a wide variety of products. Integrated circuits have continuously decreased in price and increased in performance, becoming ubiquitous in modern electronic devices. These improvements in the performance/cost ratio result, at least in part, from miniaturization, which enables more semiconductor dies to be produced from a wafer with each new generation of the integrated circuit manufacturing technology. Furthermore, the total number of the signal and power/ground contacts on a die generally increases with new, more complex die designs. An increased number of contacts on a die (e.g., pads or solderballs) over a decreased size of the die necessitates smaller contacts.
Prior to shipping an integrated circuit die to a customer, the performance of the integrated circuit is tested, either on a statistical sample basis or by testing each die. An electrical test of a semiconductor die typically includes powering the die through the power/ground connectors, transmitting signals to the die input (I) connectors, and measuring the resulting signals at the die output (O) connectors. Therefore, during the integrated circuit test at least some connectors on the die must be electrically contacted to connect the die to a source of power and a source of the test signals.
FIG. 1A is a side view of a conventional test contactor 10a in contact with a semiconductor device 10b (e.g., a device under test). The semiconductor device 10b can include a packaged die 12 attached to a die substrate 18 with a die attach material 16. Wirebonds 14 provide electrical connections between circuits in the die 12 and solderballs 20 (or pads or other contact structures) that provide communication between the die 12 and other devices. The solderballs 20 also provide communication between the die 12 and the test contactor 10a. As shown in FIG. 1A, the test contactor 10a has an array of spring-loaded pins 22 between a contactor substrate 26 and the solderballs 20. As the contactor substrate 26 moves downwardly toward the semiconductor device 10b, the pins 22 make contact with the solderballs 20. When the contactor substrate 26 moves further toward the semiconductor device 10b or the semiconductor device 10b moves toward the contactor substrate 26, the springs of the pins 22 compress, producing increased contact forces between the pins 22 of the contactor 10a and the solderballs 20 of the semiconductor device 10b. In general, the contact forces should be high enough to allow the pins 22 to break through an oxide layer on the pads/solderballs (e.g., the contact structures), but not so high as to damage the pads/solderballs. This may be a difficult requirement for the conventional spring loaded pins 22 because they tend to produce high contact forces, thus penetrating through the oxide layer on the pads/solderballs 20, but also possibly damaging the contacts on the die. Furthermore, for a large number of pads/solderballs 20, the total contactor force can quickly become very high, thus requiring powerful mechanisms to compress the contactor 10A.
FIG. 1B illustrates several designs for commercially available spring loaded pins positioned in a compressed state. In one example, a pin 22a has a pair of cylindrical, male/female pin segments 40a/41a that can slide relative to each other along a common centerline. As the contactor substrate (shown in FIG. 1A) pushes the female pin segment 41a toward the solderball 20a, a spring 32a becomes compressed between a shoulder 38a on the female pin segment 41a and a shoulder 36a on the male pin segment 40a. The contact force between a crown tip 34a and the solderball 20a increases generally linearly with the compression of spring 32a. 
In another spring loaded pin design, also shown in FIG. 1B, a pin 22b includes a spring 32b that is compressed between a shoulder 36b on a pin segment 40b and the connector substrate (shown in FIG. 1A). The pins 22a/22b typically have either a crown tip 34a or a pointed tip to facilitate breaking through the oxide layer over the solderballs 20a or pads 20b respectively. The range of compression for the springs 32a/32b is ultimately limited either by a full compression of the springs or by the force provided by a compression mechanism. The individual pins are arranged in a contactor that keeps the pins aligned in a proper layout, as explained below with reference to FIG. 1C.
FIG. 1C is a bottom view of the contactor 10a used for contacting the semiconductor device 10b (shown in FIG. 1A). The contactor 10a has a two dimensional array of pins 22 corresponding to the array of contact structures on the packaged device under test. The pins 22 protrude through a perforated mask 46. The contactor substrate 26 mechanically supports one end of the pins 22 while the opposite ends of the pins 22 engage with the device under test. Alignment features 44a-b can align the device under test and the contactor 10a. The contactor substrate 26 also provides electrical signals to the pins 22. A characteristic diameter of the pins 22 generally scales with a characteristic dimension of the contact structures on the semiconductor die or the package. Therefore, as the contact structures on the die become smaller and/or have a smaller pitch, the pins must become smaller, too. It is difficult to significantly reduce the diameter and pitch of the spring loaded pins, however, because of the difficulties in machining and assembling such small parts, which in turn can cause inconsistent performance from one assembly to another.
FIG. 2A is an isometric view of a test contactor 10c suitable for a bare die test (i.e., suitable for testing un-packaged dies). The test contactor 10c has a two-dimensional array of flexible needles 52 carrying needle blades 54 and corresponding to the layout of the pads/solderballs on the die under test. The flexible needles 52 can be curved to provide springiness when the needle blades 54 engage with the corresponding pads/solderballs on the die. The opposite ends of the flexible needles 52 are mechanically and electrically connected with a substrate 56 and further to a source of signals and/or power/ground. As the needle blades 54 engage with the corresponding pads/solderballs, the needle blades may slide over the surface of the pads/solderballs. This sliding action, coupled with a relatively high stiffness of the flexible needles 52, typically works well to break the oxide layer on the pads/solderballs, but it can also cause penetration damage, as illustrated in FIG. 2B described below.
FIG. 2B is a top view of a solderball 22 after undergoing the test described with reference to FIG. 2A. As shown in FIG. 2B, the pressure and/or sliding action of the needle blade 54 produced a depression 62 in the solderball 22. Such an undesired depression can be exacerbated by repetitive tests requiring multiple contacts or “touchdowns” between the needles 52 and the contact structures on the device. Repetitive tests are common with, for example, devices that marginally pass or fail an initial test (therefore requiring additional testing), devices placed close to a wafer edge (therefore undergoing multiple contacts due to a contactor design that does not allow for an overhang over the wafer edge), devices subjected to multiple test suites using different testers (therefore also requiring multiple contacts), etc. Furthermore, conventional test contactors have relatively high electrical resistances, which limits their ability to test high current devices. Accordingly, there remains a need for cost effective test contactors that do not damage the contact structures on the die and that can scale down in size with the contact structure size and pitch, while being capable of delivering high electrical currents.
Many semiconductor dies undergo testing prior to die singulation (i.e., testing is performed on the wafer) as well as after being packaged. Testing the semiconductor dies on the wafer helps in eliminating as many out-of-spec devices prior to investing more money and time in their singulation and packaging. However, in some cases the devices cannot be fully tested while on the wafer. For example, with high speed devices the I/O frequencies and power delivery may be too high for the typically long and slender needles 52 having high inductance and/or resistance. Therefore, in many cases after the die singulation and packaging, the packaged devices are tested again to verify performance at higher frequencies and higher power consumption. Some packaged devices may fail the test even though they passed the lower frequency/power test on the wafer. This process increases the overall manufacturing cost not only because the device was tested twice, which carries a cost penalty by itself, but also because when a packaged device fails, both the die and the package must be discarded. Thus, the package cost of the failed device cannot be recovered, which further increases the cost of testing. Accordingly, there remains a need for the test contactors that can test devices on the wafer at increased I/O frequencies and power to reduce or minimize additional testing of the packaged devices.